1. Field of the Invention
The present invention relates to an image reading apparatus equipped with an illuminating device, and an image forming apparatus.
2. Description of the Related Art
Conventionally, an image reading apparatus (original reading apparatus) is provided with an illuminating device for illuminating an original on a read line-by-read line basis. Many of illuminating devices of this type have conventionally been using a halogen lamp, a xenon lamp, or a like light source. Recently, as a more efficient light source than the conventional ones, there has been proposed a light source which uses an LED array comprised of a plurality of LEDs (Light Emitting Diodes) in a linear arrangement (e.g. in U.S. Pat. No. 5,767,976).
However, the prior art suffers from the following problem:
When a white LED array formed by arranging a plurality of white LEDs is used as an illuminating device for a color scanner, the arranged individual white LEDs sometimes have different tints (chromaticities) from each other due to their structures, thereby causing a tint variation in the LED array.
A white LED produces its white light by coating of a yellow phosphor (or red and green phosphors) on a blue light emitting element. Therefore, the tint thereof can be largely changed by the balance between the light intensity of the LED and the amount of coating of the phosphor. Therefore, white LEDs are not optimum for an illuminating device for a color scanner.
To solve the above problem, it is possible to realize an LED array with little tint variation if white LEDs having the same tint are selectively used. However, the selecting operation thereof largely increases the cost of the LED array, which makes the illuminating device expensive.
Further, even if a light source has a color variation, by correcting image data obtained by reading an image, it is possible to eliminate influence of the color variation on output image data. However, although a reference color (mainly white) used in the correction can be corrected to an accurate chromaticity, intermediate colors can have different tints (chromaticities) from the actual ones of an original.